Back-up alarms are often built into large vehicles such as heavy duty trucks and construction equipment. The alarm monitors vehicle motion, and whenever the vehicle moves in reverse, emits a clearly audible alarm signal. The signal serves as a warning to nearby persons that the vehicle is backing up and that the driver may not be able to see persons standing in the way.
Vehicle back-up alarms generally comprise two sub-systems: a motion detect circuit for sensing if the vehicle is moving in reverse; and, an alarm sounding circuit responsive to the detect circuit for emitting an alarm signal when the vehicle is moving in reverse. In some alarms, the detect circuit includes sensors for monitoring the position of the transmission lever, e.g., forward or reverse. Other alarms include sensors for monitoring the motion of some part of the vehicle's drive train, e.g., the drive shaft or a wheel. In either situation, it is necessary to assemble the alarm so that at least some part of the detect circuit is attached to a moving element of the vehicle. This makes installing a back-up alarm a complicated and expensive endeavor. Moreover, should the alarm malfunction, accessing the detect circuit sensing components to determine if they are the source of the problem can be difficult, time consuming and costly.
The alarm sounding circuit in most vehicles is a bell or horn assembly that is typically located in the rear of the vehicle so that the alarm can be heard by persons around that portion of the vehicle. This location is typically spaced some distance from the detect circuit and its sensors. This necessitates having to provide a relatively long conductive link between the detect circuit and the alarm sounding circuit. This link must be appropriately protected, since many vehicles that require back-up alarms are operated in environments where rocks and the like can be thrown up against the vehicle. These objects can quickly cause unprotected wires to break. The need to provide such a protected conductive link further adds to the complexities and costs of providing a back-up alarm.
Moreover, most back-up alarms needed to be attached to a vehicle's electrical system in order to receive the power necessary to activate the components forming the alarm system. Attaching an alarm to a vehicle so that it is connected to the electrical system further adds to the complexities of installing and maintaining the alarm.